1 Field of the Invention
This invention relates to the chemistry of carbon compounds and, in particular, to derivatives of carbohydrates that comprise modified glycosides. The materials of the instant invention may also be considered as ethers derived from cellulose or ethers derived from starch.
The invention relates moreover, in particular, to nonionic surface-active agents and to biodegradable detergents.
2. Description of the Prior Art
Nonionic surface-active agents made with the use of one or more alkylene oxides are well known. Moreover, nonionic surface-active agents based upon dextrose or another carbohydrate (providing the hydrophilic moiety), reacted with a fatty-acid-based or other similar long-chain material (providing the hydrophobic moiety) are also well known. Although the vast majority of nonionic surfactants known before the present invention can be used in mildly alkaline media, they are usually unsatisfactory for use in alkaline media of some considerable or great strength. In, for example, an aqueous solution containing 5 or more weight percent of an alkali-metal hydroxide, and especially whenever the composition is heated and/or is kept for a period of time, most nonionic surfactants tend to degrade and darken. Moreover, many of the nonionic surfactants have only limited solubility in moderately strong electrolyte solutions.
Although since about 1964, one supplier of nonionic surfactants has marketed a product which has substantially stability and solubility in moderately strong caustic soda solutions, the precise chemical composition of such product and the method for making such product have not been known to the public. Such product has been used in various ways, including incorporating it along with foam-forming agents into a moderately strong aqueous solution of caustic soda to form a foam-type caustic cleaning agent. Such an agent is used by forcing it through a foaming nozzle onto a surface to be cleaned, such as a greasy wall, and then some time later washing the wall with a stream of water. U.S. Pat. No. 3,547,828 is believed to describe a composition somewhat similar to that of the above-mentioned caustic-soluble nonionic surfactant product.
Also belonging to the prior art is U.S. Pat. No. 3,737,426, which teaches that biodegradable nonionic surfactants may be obtained from starch-derived glycosides by reacting a starch first with a number of moles of short-chain epoxyalkane such as ethylene oxide or propylene oxide (5 to 22 moles of such short-chain epoxyalkane per mole of anhydroglucose unit of starch), and then reacting that product with about one to three moles, per anhydroglucose unit, of a long-chain epoxyalkane containing 6 to 18 carbon atoms. The patent teaches that such a nonionic surfactant has one or more "hemiacetal linkages" (more properly, acetal linkages) in place of the usual polyether linkages and it appears that, accordingly, such a "hemiacetal-linked" non-ionic surfactant is considerably more readily degraded by enzymes present in sewage or raw river water, i.e., such a surfactant is considerably more highly biodegradable. Although the patent contains figures that indicate that its composition must have, in water, relatively excellent surfactant properties, it contains nothing that would indicate to a person of ordinary skill in the art that its compositions would be soluble to any appreciable extent in moderately strong solutions of caustic soda or other electrolytes. Most compounds having a polyoxyalkylene structure are notably poor in solubility in such alkali solutions.
Considerably earlier, it had been taught in U.S. Pat. No. 2,407,002 that is was possible to make glycol glucosides and then to react them with alkylene oxides but, in this reference, it was taught that the preferred alkylene oxides are ethylene oxide and propylene oxide; there is nothing to lead a person of ordinary skill in the art to believe that he should disregard the teachings of the patent and use a higher alkylene oxide or similar glycidyl ether to obtain an alkali-soluble nonionic surfactant.
Also in the prior art is U.S. Pat. No. 3,772,269, which teaches the making of a mixture of a higher-alkyl glucoside and a glycol glycoside in a one-step process. The compositions produced in the patent are indicated as having some surfactant properties, as evidenced by foam values, but nothing in the patent indicates to persons of ordinary skill in the art that its compositions have any substantial solubility in caustic soda or other electrolytes.
In the prior-art nonionic surfactants of which I am aware, there has frequently been reliance upon a joining of the hydrophobic part of the molecule to a remaining part of the molecule through an acetal linkage, such that when the linkage is destroyed, the molecule is cleaved into separate parts which are relatively highly hydrophilic and hydrophobic and are thus no longer themselves surface-active to any appreciable extent. Moreover, such acetal linkages are rather readily severed, especially under acidic conditions. Ether linkages are far more stable. The surfactants of the present invention are believed to comprise molecules in which long-chain alkyl epoxides or other oxirane-containing hydrophobes have been caused to add themselves through an ether linkage to one or more of the hydroxyl groups of the ring or the central portion of a glucosyl unit, rather than merely being connected to the glucosyl unit in question through an acetal linkage, and it is thus believed that as a result of this difference in the chemical structure of the nonionic surfactant product, there are obtained with this invention products which have the ability to continue to exhibit surfactant properties despite the use of the surfactant in various media or under various conditions which would cause any surfactant relying upon an acetal linkage between its hydrophobic and hydrophilic parts to discontinue acting as a surfactant. In this regard, the surfactants of this invention present themselves as being distinguishable from those of U.S. Pat. Nos. 3,547,828; 3,772,269; and 3,737,426.
The invention is at the same time, however, able to be distinguished chemically from other ether-linked non-ionic surfactants not containing any glucosyl units, in that these frequently contain chains of ether-linked lower oxyalkylene units and are often characterized by having little or no stability or solubility in moderately strong alkaline media. In this regard, the surfactants of this invention present themselves as being distinguishable from those of U.S. Pat. Nos. 2,677,700; 2,674,619; 2,979,528; and 2,213,477.